Electrical connectors are known which include a plurality of electrical contacts having exposed contact sections for electrical connection to circuits of a circuit element, such as conductive traces disposed on a major surface of a printed circuit board. U S. Pat. Nos. 4,903,402 and 4,925,400 disclose similar such connectors which include two arrays of contacts each associated with respective arrays of conductive traces of printed circuit elements secured to opposed sides of a common central cooling plate of a module such as a line replaceable module (LRM), the connector being secured by fasteners to the cooling plate at an end thereof; the plate, the circuit cards and board-mounted components thereon, and the connector are disposed within protective covers of the module, with the connector having a mating face exposed at the end of the module for mating to another connector.
Arrays of such modules are commonly used in electronics units such as black boxes aboard aircraft, each matable with connectors on a mother board within the unit or box. The contacts are conventionally connected to the conductive traces of the circuit cards by their contact sections being soldered thereto in a surface mount arrangement; the contact sections are defined proximate free ends of elongate cantilever arms. The connector is mounted within the module in such a manner as to be incrementally movable transversely with respect to the module covers and the circuit cards affixed to the cooling plate, upon mating when the module is inserted into the electronics unit or black box; the elongate cantilever arms are flexible, and the incremental movement does not disturb nor overstress the soldered connections of the contacts to the conductive traces of the circuit cards.
U.S. Pat. No. 4,903,402 also discloses a method of assembling the connector to the circuit cards previously affixed to the cooling plate, and a method of fabricating the connector to facilitate such assembly. The plurality of contacts of a row are stamped and formed while on a continuous carrier strip, as is conventional and the contact sections are precisely spaced apart a selected distance. The carrier strip is joined to the contacts of a row at the free ends of the elongate cantilever arms beyond the contact sections, which are formed into convex shapes enhancing fillet formation of the solder joints. Several rows of contacts associated with a single printed circuit element are to have their contact sections in a common plane to be joined to respective traces on a common surface of the circuit card; the carrier strips of the several rows are joined integrally together after the spaced contact sections of each row are registered with respect to those of the other rows to attain the desired spacing matching that of the trace array to which they will be soldered; the multirow array of contacts of the connector are handled as a unit during connector fabrication. The joined carrier strips are maintained on the arm free ends until after soldering is complete, whereafter the joined strips are carefully broken away in a manner not disturbing the solder joints. The method disclosed maintains the contacts precisely spaced apart to match the close spacing of the traces (such as 0.025 inches between trace centerlines), and minimizes tendencies of the elongate cantilever arms to be bent or broken or their spacing disturbed during handling prior to soldering, and thus eliminates the need for alignment tooling at the soldering operation of the type necessary to realign and again precisely space the contact sections of the individual arms to match the respective closely spaced traces.
In U.S. Pat. No. 4,852,252 electrical contact terminals are disclosed to be soldered to discrete wires after the terminals have been disposed within a dielectric housing, and the terminations sealed from the environment. The solder tail contact section of each terminal extends rearwardly from the housing rearward face; a length of heat recoverable dielectric tubing containing an annular preform of solder centrally along its length placed over the solder tail; the stripped end of the conductor wire is superposed over the solder tail within the tubing, and the solder preform is positioned around the superposed solder tail/wire end. The solder is then melted and flows around the solder tail and wire end, forming a solder joint electrically joining the wire and the terminal; the heat recoverable tubing shrinks in diameter until adjacent the portion of the conductor wire and the terminal within the tubing, and sealant material at ends of the tubing melts and seals the ends of the tubing to the wire insulation and dielectric material of housing flanges extending along a portion of each terminal exiting the housing sealing the termination and exposed metal from the environment.
U.S. Pat. No. 4,852,252 further discloses providing the terminals each with a thin layer of magnetic material along the surface of the nonmagnetic low resistance solder tail of the terminal facing away from the surface to which the wire end will be soldered; in U.S. patent application Ser. No. 07/385,643 filed Jul. 27, 1989, now U.S. Pat. No. 4,995,838 a preform of foil having a magnetic layer is disclosed to be soldered to the terminal solder tail's wire-remote surface. The bimetallic structure uses the Curie temperature of the magnetic material to define an article which will generate thermal energy when subjected to radiofrequency current of certain frequency for sufficient short length of time until a certain known temperature is achieved, above which the structure is inherently incapable of rising; by selecting the magnetic material and sufficient thickness thereof and selecting an appropriate solder, the temperature achieved can be selected to be higher than the reflow temperature of the solder preform; when the terminal is subjected through induction to RF current of the appropriate frequency, the solder tail will generate heat which will radiate to the solder preform, reflow the solder, and be conducted along the wire and the terminal and radiate further to shrink the tubing and melt the sealant material. The terminal thus includes an integral mechanism for enabling simultaneous soldering and sealing without other application of heat; excess heat is avoided as is the potential of heat damage to remaining portions of the connector or tubing.
Another U.S. Pat. No. 4,789,767 discloses a multipin connector whose contacts have magnetic material layers on portions thereof spaced from the contact sections to be surface mounted to respective traces on the surface of a printed circuit board. An apparatus is disclosed having a coil wound magnetic core having multiple shaped pole pieces in spaced pairs with an air gap therebetween within which the connector is placed during soldering. The pole pieces concentrate flux in the magnetic contact coating upon being placed beside the contact sections to be soldered, to transmit RF current to each of the contacts, generating thermal energy to a known maximum temperature to reflow the solder and join the contact sections to the conductive traces of the printed circuit element.
Such Curie point heating is disclosed in U.S. Pat. Nos. 4,256,945; 4,623,401; 4,659,912; 4,695,713; 4,701,587; 4,717,814; 4,745,264 and European Patent Publication No. 0241,597. When a radio frequency current for example is passed through such a bipartite structure, the current initially is concentrated in the thin high resistance magnetic material layer which causes heating; when the temperature in the magnetic material layer reaches its Curie temperature, it is known that the magnetic permeability of the layer decreases dramatically; the current density profile then expands into the non-magnetic substrate of low resistivity. The thermal energy is then transmitted by conduction to adjacent structure such as wires and solder which act as thermal sinks; since the temperature at thermal sink locations does not rise to the magnetic material's Curie temperature as quickly as at non-sink locations, the current remains concentrated in those portions of the magnetic material layer adjacent the thermal sink locations and is distributed in the low resistance substrate at non-sink locations. It is known that for a given frequency the self-regulating temperature source thus defined achieves and maintains a certain maximum temperature dependent on the particular magnetic material. One source for generating radiofrequency current such as of 13.56 mHz is disclosed in U S. Pat. No. 4,626,767.
The conductive substrate can be copper having a magnetic permeability of about one and a resistivity of about 1.72 micro-ohm-centimeters. The magnetic material may be for example a clad coating of nickel-iron alloy such as Alloy No. 42 (42% nickel, 58% iron) or Alloy No. 42-6 (42% nickel, 52% iron and 6% chromium). Typical magnetic permeabilities for the magnetic layer range from fifty to about one thousand, and electrical resistivities normally range from twenty to ninety micro-ohm-centimeters as compared to 1.72 for copper; the magnetic material layer can have a Curie temperature selected to be from the range of between about 200.degree. C. to about 500.degree. C., for example. The thickness of the magnetic material layer is typically one to three skin depths; the skin depth is proportional to the square root of the resistivity of the magnetic material, and is inversely proportional to the square root of the product of the magnetic permeability of the magnetic material and the frequency of the alternating current passing through the two-layer structure. Solders can be tin-lead such as for example Sn 63 reflowable at a temperature of about 183.degree. C. or Sb-5 reflowable at a temperature of about 240.degree. C. Generally it would be desirable to select a Curie temperature of about 50.degree. C. to 75.degree. C. above the solder reflow temperature.
It is desirable to simplify the process of soldering contact sections to circuit traces.
It is also desirable to eliminate the need at soldering to realign the individual ones of the plurality of contact sections at ends of elongate cantilever beam arms, and the combing tooling necessary to such individual arm realignment.
It is especially desirable to perform soldering in a process not subjecting all portions of the printed circuit element and the connector to the high temperatures requisite to reflow solder.
It is further desirable to simplify the providing of solder at discrete solder joint sites for such soldering.